1. Field of the Invention
This invention relates generally to an improved blade design for fluid driven turbines, and more particularly, but not by way of limitation, to an improved windmill which includes a self-governing turbine blade system and an improved apparatus for coupling the turbine to an electric generator.
2. Description of the Prior Art
A major factor in the design of any fluid powered turbine is the velocity of the fluid. The fluid velocity must be high enough to overcome the static frictional forces in the turbine and initiate the rotary motion of the turbine. The fluid velocity must not be so high as to turn the turbine at a rotational speed higher than that for which it is designed. It is most desirable for the fluid velocity to be such that the turbine uses the available energy, in the moving fluid, as efficiently as possible. For a fluid turbine operating at a constant fluid velocity it is relatively simple to design the turbine to accommodate these considerations. It is much more difficult, however, to design a turbine which will operate satisfactorily over a wide range of fluid velocities.
One type of fluid powered turbine which is particularly subject to the problems of varying fluid velocity is the windmill. The fluid velocity, in this case the wind velocity, is entirely uncontrollable. The windmill is subject to wind velocities varying from zero, on a calm day, to perhaps one hundred miles per hour, in a raging storm. It is desirable that the wind velocity required to start the windmill be as low as possible so that the windmill will operate in a relatively light breeze. The windmill, however, must be designed to withstand the high winds of a hurricane or other storm; this generally requires that the windmill be governed in some manner to limit its rotational speed. Additionally, it is desirable that the windmill operate most efficiently at a wind velocity close to that of the average wind velocity of the locale.
Several devices for starting the windmill or assisting its operation at low wind velocities have been previously proposed. Cullin U.S. Pat. Nos. 2,159,886 and McDonald U.S. Pat. No. 2,086,279, disclose the utilization of an electric motor to start the windmill in operation at wind speeds high enough to keep the windmill in motion, but too low to overcome the initial resistance to motion.
U.S. Pat. No. 1,941,611 issued to Manikowske discloses the use of a coupling device, actuated by centrifugal force, which permits a turbine blade to be initially uncoupled from an electric generator, thereby reducing the windspeed required for start-up, and then upon the attainment of a predetermined rotational speed, the device couples the turbine blade to the generator.
The prior art has also included numerous devices for governing the speed of the turbine blade at high wind speeds. The Manikowske patent describes the use of a centrifugally actuated device which uncouples a turbine blade from an electric generator at a predetermined rotational speed so that the generator will not be oversped at high wind velocities. Halkias U.S. Pat. No. 1,483,301 teaches the use of an electrical feed-back circuit which senses whether the rotational speed is above or below a predetermined norm, and correspondingly actuates solenoid devices which adjust the turbine blades or vanes to reduce or increase the force exerted on the turbine blades by the wind. U.S. Pat. No. 1,334,385 issued to Clipfell, et al. teaches the use of a centrifugally operated device to automatically vary the pitch of the blades as the windspeed varies, so as to prevent overspeeding of the turbine in high winds.
U.S. Pat. No. 924,060 issued to Hards discloses the use of a spring loaded mounting of the turbine blades which permits the blades to yield and feather in a gust of wind, thereby preventing overspeeding of the turbine.
All of the previously proposed devices discussed above used rather complex apparatus to achieve low speed start-up and high speed governing. I have, however, invented an improved turbine blade system which will operate at low wind speeds and which is self-governing at high wind speeds without the use of any moving parts. This is accomplished by combining two sets of turbine blades. The first set of blades operates efficiently at relatively low wind speeds, but is less efficient at relatively high wind speeds. If driven at a rotational speed higher than some predetermined speed, the blades in this set will actually cease operating as a turbine and will begin pumping air against the direction of the wind movement. The second set of turbine blades is designed so as to be especially effective at relatively high wind speeds.
At very low wind speeds, the effect of the first set of blades is predominant, and the wind force exerted on those blades will cause the windmill to start turning. With increasing but relatively intermediate wind speed, both sets of blades act as turbines and the forces exerted thereon turn the windmill at ever increasing rotational speeds. At still higher wind speeds, above some predetermined, relatively high velocity, the effect of the second set of blades becomes predominant, and if unrestrained would continue to increase the rotational speed of the windmill above that for which it is designed. At this point, however, the first set of blades acts as a pump, pushing air in a direction opposite the direction of the natural wind movement, thereby lessening the energy input to the rotating windmill. At some given wind speed, the combined effects of the first and second sets of blades will be such that a constant maximum rotational velocity is achieved. Even if the wind speed further increases, the windmill will turn no faster.
Additionally, I have devised an improved variable friction generator drive system which further enhances the low speed start-up capabilities of my invention.
Devices are known which might initially appear superficially similar in their structural make-up, but upon more thorough inspection it is readily seen that those devices operate in a significantly different manner to achieve results entirely unlike those of the present invention. Thus, for example, Cullin U.S. Pat. No. 2,278,247 shows a wind turbine having two sets of blades. Both sets of blades are designed so as to act as turbines to turn a generator at the wind speeds for which it is designed, but there is no balancing effect between the two sets of blades acting to govern the speed of the turbine. Rotational speed of that device is governed only by varying the pitch of the outer set of blades. Furthermore, the inner set of blades in the Cullin structure are primarily for the purpose of directing air through the turbine to cool the electric generator located behind it.
U.S. Pat. No. 1,804,016 issued to Koenig shows another apparatus having two sets of blades. The Koenig apparatus is a propeller which is used to pump water or air and thereby drive a boat or an airplane. The inner set of blades was added to the Koenig device merely to increase the efficiency of the propeller along its radially inner portions where the outer set of blades was not very efficient. Both sets of blades act in the same manner, that is they both pump air, so that there is no balancing effect between the two sets of blades.